A pump of this type is especially known in document EP-A-0 453 357. This pump comprises a control rod traveling in a pump body. The piston in the form of an elastic moldable sleeve is mounted on the control rod. This piston slides in a tight or sealing manner against the inner wall of the pump body and likewise closes the intersecting ducts which lead to the inner duct of the control rod. The upper end of the sleeve which forms the piston is a catch support for the shoulder that forms the control rod. Thus, as soon as the pressure increases to a satisfactory level, the sleeve is formed by resting on the catch support for the control rod collar so that the pressurized fluid in the pump chamber flows through these intersecting ducts and the inner duct of the control rod. In the pump described in this document (EP-A-0 453 357), the piston/sleeve is therefore always subjected to stress which occurs at the top of the sleeve between the shoulder catch device of the control rod and the tight duct of the piston lip with the inner section of the pump body. Accordingly, the sleeve is likely to get out of shape with the effect of this permanent stress so that it no longer seals perfectly tightly the intersecting ducts of the control rod.
Another pump of the same type is known from document FR-1 544 683. The pump described in this document likewise includes a control rod on which is mounted a piston in the form of a sleeve. The piston comprises tightness lips with an impenetrable slide against the inner section of the pump body. The sleeve seals tightly the intersecting ducts which lead to the central duct of the control rod. In a manner similar to the document cited above, the top end of the sleeve supports the shoulder that forms the control rod. The sleeve comprises a section of less thickness which gives it a certain elastic deformability. This elastic deformability is for the purpose of clearing intersecting ducts when the inner pressure of the pump chamber reaches an adequate level. There again, the sleeve is permanently subjected to an axial stress which occurs between the shoulder support of the control rod and another lower support which likewise forms the control rod right below the intersecting ducts.
We are likewise familiar with other pumps of this type using a free floating sleeve piston mounted on the control rod. Certain ones use a precompression spring that require the piston to be in a position that is suitable for sealing the control rod intersecting ducts. We can specifically cite document FR-A-2 399 286. Other pumps using earlier techniques do not use any device that calls for the free floating piston so that there is no precompression.
The purpose of the present invention is to reduce the difficulties cited above regarding earlier techniques by defining a precompression, hand-operated pump in which the piston sleeve is not subjected to any permanent stress, and that accordingly, exhibits a stronger resistance to wearing out.
In order to attain this goal, the purpose of the present invention is to provide a hand-operated pump for fluid distribution comprising:
a pump body defining a pump chamber with an inlet valve,
a hollow control rod traveling in the pump between a lock position and a drive-in position or depressed position, said rod being biased to the lock position by a return spring, said rod comprising an inner lift duct,
a free floating piston assembled in a sliding manner in the pump body on the control rod,
the piston and rod serving to define an outlet valve for sealing the inner lift duct in the lock position,
the outlet valve exhibiting a cylindrical sealing contact or tight contact which is adapted to become loose by sliding the piston towards the top on the rod at a determined height.
The present control rod has a tapered surface extending outwardly on which the piston acts during its sliding towards the top. The combination of a cylindrical sealing contact or tightness contact exhibiting a certain height and a tapered functioning surface on which the piston is mounted during its sliding towards the top with the pressure effect extending in the pump chamber allows for obtaining a precompression which is dependent on the top of the cylindrical contact, on the conical angle of the tapered surface and on the material forming the piston. Because of the tapered surface, there can be the passing through said precompression spring whose purpose is to force the piston towards the bottom.
According to the layout shape, the piston comprises a sleeve surrounding the control rod, said sleeve exhibiting a lower part in cylindrical tight contact or sealing contact with the control rod and a higher end adapted to function on the tapered rod surface when the piston slides toward the top.
In contrast, in pumps using previous techniques, the sleeve was bent out of shape by deflection by supporting its upper end against the support collar, while in the present invention, the upper end of the sleeve can slide. In the present invention, the upper end of the sleeve can slide on a tapered surface by undergoing radial distortion. The use of a tapered surface allows for a standard constant sleeve distortion, whereas, with the previous technique devices, it was difficult to reduce sleeve deflection. The result is that it is easier to determine the force that is necessary to apply to the sleeve to use it at a certain distance on the tapered surface. Thus, with a defined moldable material, it is possible to determine the conic angle of the tapered surface and the height of the cylindrical tight contact so as to obtain adequate precompression.
In order to improve cylindrical tightness, the control rod comprises materials to radially compress the lower end of the sleeve.
In accordance with the layout shape, the control rod has, at its lower end, a peripheral compression device allowing for the compressing of the lower end of the sleeve between the rod and said peripheral device.
Advantageously, the peripheral compression device comprises a rod-concentric cylindrical surface, thus defining a unitxe2x80x94a reception groove with tight clamping for the lower part of the sleeve, linking the inside of the control rod with the pump chamber.
Thus, the height of the concentric cylindrical surface for the peripheral compression device determines the height of the lost motion during which the sleeve remains in tight contact with this concentric cylindrical surface and thus seals the outlet valve.
In accordance with another characteristic of the invention, the piston comprises a peripheral shoulder located at an intermediate level between the higher end and the lower end of the collar, said shoulder resting against a stationary element of the pump when the rod is in a lock position so that the sleeve is not in a compression state when locked.
In accordance with another aspect of the invention, the piston comprises an outer peripheral tightness bead or cord adapted to slide tightly against an inner cylindrical section from the lock position to the proximity of the lower or depressed position where the cord leaves said section thus to allow for venting of air only at the end of the stroke.
The invention will now be described more comprehensively with reference to the attached drawings giving by way of a non-limiting example a layout mode for the present invention.